1. Field of the Invention
This invention relates generally to tube bending machines. More particularly, the invention relates to an automatic clamping assembly for a bend arm of a tube bending machine.
2. Description of the Related Technology
In order to accomplish the bending of pipes or tubes in a mass production environment, automated pipe or tube bending machines have been developed. The workpiece to be bent may be of relatively large diameter, such as an automobile or truck exhaust pipe, or may be of relatively small diameter, such as a tube for a hydraulic or pneumatic apparatus.
A tube bending machine (“bender”) usually forms a series of pre-programmed bends in a length of tube. A bender typically has a fixed, elongated machine bed configured to support and advance a workpiece to a tube bending zone (the “bend head”) at one end of the machine bed. The workpiece is fed, such as from a length of tubing or a coil, through a rotatable chuck or collect gripping arrangement to the bend head. Typically, the bend head includes a rotary bend die having a concave groove corresponding to a radius of the diameter of the workpiece to be bent. The tube is fed toward the bend head until the tube is positioned at the bend die at the location to be bent. A bend arm assembly then positions a clamp die, which has a concave groove corresponding to the concave groove of the bend die, into abutting relation with the tube at the bend point. In one common type of machine, force is then applied to the clamp die to physically restrain the tube at the bend die. Rotation of the bend and clamp dies, with the tube clamped between them, bends the tube around the bend die.
The clamp die is typically coupled to a moving slide which moves in and out between closed and open positions of the clamp-bend-dies pair. In one configuration, the clamp die is mounted on a linkage mechanism which drops away, below the centerline height of the bend die, into a cavity of the bend arm when in an open position to clear the tube after bending. The clamp die is usually positioned with a hydraulic cylinder which operates at a single pressure. A limit switch indicates when the clamp die is fully closed. This system usually involves the coupling of the clamp die holder on a toggle mechanism, which means that the applied pressure cannot be varied and is relatively difficult to predict. This configuration results in a substantial disadvantage since application of excessive force results in scoring or crimping of the tube, while application of insufficient force results in slippage of the tube during pivoting of the clamp and bend dies. Either event may result in an unusable tube section.
Therefore, there is a need in the industry for a tube bending machine having a clamping assembly that provides a controllable and variable clamping force. The invention disclosed below provides various mechanisms and methods that address this need.